This invention relates to a fuel injection apparatus for an internal combustion engine and, more particularly, to a fuel injection apparatus in which fuel is atomized by air supplied through an air passage.
FIG. 6 is a schematic diagram illustrating one example of a fuel injection system of a known fuel injection apparatus for an internal combustion engine, in which an internal combustion engine 1 has an intake pipe 20 for supplying air to the internal combustion engine 1. The intake pipe 20 has an air flow throttle valve 2 disposed therein for controlling the air which flows through the intake pipe 20. The air flow throttle valve 2 divides the intake pipe 20 into a higher-pressure portion 20a and a lower-pressure portion 20b which have different air pressures. The intake pipe 20 comprises an intake manifold 20c disposed between the air flow throttle valve 2 and a cylinder 1a of the internal combustion engine 1 in the lower-pressure portion 20b of the intake pipe 20. An air flow sensor 3 is disposed in the intake pipe 20 for detecting a quantity of the air which flows through the intake pipe 20. The air flow sensor 3 is electrically connected to an electronic control unit 6 (ECU) for supplying an output signal indicative of the air flow amount to the ECU 6.
A fuel injector 4 is disposed in the intake manifold 20c and has a nozzle which faces the cylinders 1a of the internal combustion engine 1 for jetting fuel supplied from a fuel tank (not shown) by a fuel pump (not shown) to provide an air-fuel mixture the cylinders 1a of the internal combustion engine 1. The fuel injector 4 is electrically connected to the ECU 6 and operates according to pulse signals provided by the ECU 6. As seen from FIG. 6, the fuel injection apparatus also comprises an air passage pipe 5 whose one end is connected to the higher-pressure portion 20a of the intake pipe 20 between the air flow sensor 3 and the air flow throttle valve 2 and whose the other end is connected to the lower-pressure portion 20b close to the nozzle of the fuel injector 4 for impinging air at a high speed to fuel injected from the fuel injector 4 to promote an atomization of the fuel spray. Disposed at the top of the cylinder 1a are, respectively, an intake valve 7a and an exhaust valve 7b, and a piston 8 is disposed within each of the cylinders 1a.
In the known fuel injection apparatus as described above, the fuel injector 4 is supplied with fuel whose pressure is electrically controlled at a predetermined value by a pressure regulator (not shown). The ECU 6 determines a controlling duty ratio according to the output signals from the air flow sensor 3 and output signals from a cooling water temperature sensor (not shown) which may be disposed in the water jacket (not shown). Then the ECU 6 supplies pulse signals indicating the controlling duty ratio to the fuel injector 4. The fuel injector 4 opens or closes electromagnetically according to the pulse signals from the ECU 6 and jets the fuel into the cylinders 1a of the internal combustion engine 1. The quantity of the fuel jetted by the fuel injector 4 is controlled to be in proportion to the controlling duty ratio indicated by the pulse signals from the ECU 6. Therefore, fuel of the most suitable quantity can be always supplied by the fuel injector 4 according to the operating condition of the internal combustion engine 1.
Further, due to the difference of air pressure between the higher-pressure portion 20a and the lower-pressure portion 20b of the intake pipe 20 which are separated by the air flow throttle valve 2, air of a relatively high pressure is supplied at a high speed to the nozzle of the fuel injector 4 through the air passage pipe 5 and it impinges against the fuel injected from the fuel injector 4 to promote atomization of the fuel.
However, the quantity of the high-speed air flowing through the air passage pipe 5 is determined on the basis of only the difference in air pressure between the high-pressure portion 20a and the lower-pressure portion 20b of the intake pipe 20. Further, the quantity of the high-speed air is selected to be comparatively small because the engine speed of the internal combustion engine 1 cannot be made high during idling conditions because the fuel consumption becomes worse and is not economical when the idling engine speed is high. Hence, in spite of the promotion of the atomization of the fuel as described above, the quantity of the high-speed air supplied to the fuel injector for fuel atomization is not enough for the optimum atomization in all conditions except for the-idling of the internal combustion engine 1, and the particle diameter of the fuel cannot be small enough to provide a suitable combustion.
Further, the amount of fuel injection varies in accordance with the operation state of the internal combustion engine 1, such as the suction air flow rate and the coolant temperature as described above, and there is an optimum air flow rate through the air passage pipe which most suitably atomizes the fuel in accordance with the fuel injection amount. However, this optimum air flow rate cannot be realized with the known fuel injection apparatus. Therefore, the fuel consumption cannot be efficient and a lot of Hydro Carbon (HC) has been emitted undesirably.